Diode-pumped Tm:YLF MOPA system delivering 713 mJ pulse energy with near-diffraction-limited beam quality

We present a diode-pumped high-energy Tm:YLF nanosecond MOPA system at 1880nm wavelength. Using a simplified laser amplification process, we analyze the distribution of the upper-level population in the gain medium under different pump durations and beam sizes and discuss the dependence of amplifier gain on pump intensity. A cavity-dumped Tm:YLF oscillator was used as a seed source, delivering 5.5 mJ pulse energy with 15 ns pulse duration at a 1 Hz repetition rate. The pulse energy was boosted to 713 mJ using a four-pass Tm:YLF pre-amplifier followed by a double-pass dual-crystal Tm:YLF power amplifier. The system exhibits a good beam quality with M² of 1.27 and 1.13 in the horizontal and vertical directions, respectively.